Brian,
Not familiar with German Artillery procedures of the day but as an ex-Gunner I suspect they are using them as reference points, perhaps to get a bearing to the command post so they can then combine that with the distance and determine the different changes to firing data required for each gun from what we call "battery centre". This is used to "converge" the fire when you want to concentrate your fall of shot close together, rather than just linear.
They are probably still in the process of setting up the gun position and I suspect the poles would then come down.
Peter